*{
    margin: 0;
    padding: 0;
    list-style: none;
    text-decoration: none;
}
.coner{
    width: 1200px;
    margin: auto;
    height: 100px;
}
.col{
    width: 33.333333%;
    float: left;
    height: 100px;
    background: aqua;
}
.coner::after{
    content: "";
    display: table;
    clear: both;
}
@media (max-width:600px) {
    .coner{
        width: 100%;
    }
    .col{
        width: 100%
    }
}